1. Field of the Invention
This invention relates to an aircraft nacelle that comprises a reinforced outside wall.
2. Description of the Related Art
FIG. 1 shows a propulsion system 10 of an aircraft that is connected under the wing by means of a mast 12.
This propulsion system comprises a nacelle 14 in which a power plant that drives a fan that is mounted on its shaft 16 is arranged in an essentially concentric manner. For the description, the longitudinal direction corresponds to that of the axis of the nacelle that is referenced 18. The planes that are perpendicular to the longitudinal direction are called transverse planes.
As illustrated in FIG. 3, the nacelle 14 comprises a wall that delimits an inside pipe 20 that channels a stream of air to the power plant, at the front a lip 22 (forming a leading edge) and on the outside an outside wall 24 that is illustrated in detail in FIG. 2.
A front frame 26 is provided to connect the inside pipe 20 and the outside wall 24 and to support the lip 22. In addition, a rear frame 28 is provided to connect the inside pipe 20 and the outside wall 24 and to ensure the connection with the power plant M.
To reduce the noise pollution of the propulsion system, the inside pipe 20 comprises at least one acoustic treatment panel 30 that comprises—from the inside to the outside—a reflective layer, at least one alveolar structure, and at least one acoustically resistive layer that delimits the inside pipe 20 and channels the air in the direction of the power plant.
This acoustic treatment panel 30 can be equipped with a drainage system that makes it possible to discharge the water from the cells of the alveolar structure. For this purpose, the cells of the alveolar structure can comprise slots that make possible the circulation of liquids in the direction of the lower part of the panel 30. Other means can be considered for directing the liquids at the lower part of the panel 30.
Close to the generatrix of the panel 30 arranged at 6 o'clock, the reflective layer comprises a large number of openings that make possible the flow of liquids outside of the acoustic treatment panel as illustrated by the arrows 32 in FIG. 3. Thus, the drained liquids flow at the lower part of the cavity 34 that is delimited by the lower pipe 20, the front frame 26, the outside wall 24, and the rear frame 28.
As illustrated in FIGS. 2 and 3, the outside wall 24 comprises numerous circumferential stiffeners 36 for withstanding forces generated by the aerodynamic flows or possible shocks.
These circumferential stiffeners 36 come in the form of ribs projecting toward the inside of the cavity 34, as can be seen in FIGS. 2 and 3.
Each stiffener 36 constitutes a barrier that prevents the flow of liquids toward the low part of the cavity close to the rear frame 28, with the result that it is necessary to provide a large number of discharge openings 38 upstream from each stiffener so as to prevent the accumulation of water at this level.
This embodiment is not completely satisfactory for the following reasons:
During certain flight phases, partial vacuum phenomena can appear on the exterior of the nacelle and generate a pressure gradient P1<P2<P3<P4 at the surface where the discharge openings 38 are present. With the pressure inside the cavity 34 being essentially equal to the mean of pressures P1, P2, P3, and P4, there is therefore a risk of circulation from the outside to the inside of the cavity 34 at the first discharge openings 38, manifesting as stresses on the structure. To respond to these stresses, it is necessary to reinforce the outside wall 24; this is reflected by an increase in the onboard weight and therefore in energy consumption.
One solution can consist in replacing the discharge openings 38, which are located in the zone impacted by the partial vacuum phenomena, by a scoop. However, a scoop tends to increase the drag and therefore the energy consumption of the aircraft.